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Duramax to 8.1 swap

OutlawRider

OutlawRider

Gum Gardener
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May 20, 2020
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658
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Arkansas
Well I’m going to put this here. Trying to see if anyone has any info or insight into to this swap.

So here is what I have:
-Wrecked 01 2500HD Chevy ECSB low mileage for age 8.1 with brand new Allison 4x4 push button loaded
-Pretty clean 03 2500HD GMC CCSB higher mileage body, new to truck supposedly 03 Duramax (from Denali, swap unfinished) with unknown mileage/condition Allison 4x4 push button loaded.

So I bought the wrecked 8.1 to swap out the motor/tranny. That is why I bought the Duramax truck. I paid for the body only but the guy didn’t feel like pulling the motor/tranny so it stayed.

I personally don’t know much about diesels and what it would take to make this run. I plan to make this my DD (to hell with gas mileage right now). The annoying part of this swap is dealing with the computers having different VINs and anti-theft system as well as the slight difference in the wiring harness between years when it comes to the AC and oil pressure. Since I have a donor, I have all the harnesses as well as fuel system parts.

The overall goal is just to level the truck, run stocks with 35s, trim as needed, and just enjoy driving the truck to work and use it for work duty on the weekends. I have a camper and tractor it may pull, but honestly, I don’t need this much truck 99% of the time. This won’t be a forever DD and will transition to a work truck only when I buy something new.

So any heads up on this swap (other than no one else would hardly do this to a duramax)? Should I try to see what it would take to just fix the questionable Duramax (03 LB7)? Either way, I will try and document whatever I do here (especially if I swap to gas). The Duramax will most likely go into the 01 and I will try to get it going and just beat on the wrecked truck with it (wrecked truck is semi driveable).
Pics of the 2:
 

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So you want to swap a 8.1 into a truck that you plan to drive a bunch and then swap the duramax into a weekend truck to beat on instead of just finishing the install on the duramax into a duramax truck? That is a long and hard road just to end up with wrong motor's in wrong truck's. The 8.1 would be the better weekend play toy that sits between uses and duramax would be better DD that gets ran often, also they are already in the correct trucks for that. I would spend the time and money to get the duramax finished up and either drive it or sell it for profit and get a gas DD if thats what you want, then weekend toy the 8.1 or use it for parts in the gas dd you get. Diesels are bringing better money anyhow so its worth more just to sell it if you dont want diesel.
 
Since the 8.1 is wrecked, pull the running gear and either store it or sell it and finish the Duramax swap into the other one. Part out what can be from the 8.1 truck for costs towards the duramax rig.
 
Navydoc8778 said:
Since the 8.1 is wrecked, pull the running gear and either store it or sell it and finish the Duramax swap into the other one. Part out what can be from the 8.1 truck for costs towards the duramax rig.
Click to expand...
350TacoZilla said:
So you want to swap a 8.1 into a truck that you plan to drive a bunch and then swap the duramax into a weekend truck to beat on instead of just finishing the install on the duramax into a duramax truck? That is a long and hard road just to end up with wrong motor's in wrong truck's. The 8.1 would be the better weekend play toy that sits between uses and duramax would be better DD that gets ran often, also they are already in the correct trucks for that. I would spend the time and money to get the duramax finished up and either drive it or sell it for profit and get a gas DD if thats what you want, then weekend toy the 8.1 or use it for parts in the gas dd you get. Diesels are bringing better money anyhow so its worth more just to sell it if you dont want diesel.
Click to expand...
I guess my issue with the Duramax is the lack of knowledge on:
A) Diesels in general
B) The condition of the engine and trans itself.
C) The cost to maintain a diesel, especially one with known injector problems.

The non-wrecked truck was supposed to just be a body that happened to include an engine and transmission.

I was thinking sell the engine and transmission for what I even had into the truck. Hell if they were running, I could sell them for more than what I have into both trucks.
 
been looking into a Duraburb swap for my 2002... may be interested in the Dirtymax and all the extras...
 
What are you calling high mileage on the diesel truck?


I'm always looking for under valued stuff, and it seems that buying an lb7 duramax with 200-250k that needs injectors, that nobody else wants, then installing $2k of high quality injectors and getting another 100k from the truck, is possibly the best dollar for dollar value in the entire truck market
 
backchat said:
been looking into a Duraburb swap for my 2002... may be interested in the Dirtymax and all the extras...
Click to expand...
Projectjunkie said:
What are you calling high mileage on the diesel truck?


I'm always looking for under valued stuff, and it seems that buying an lb7 duramax with 200-250k that needs injectors, that nobody else wants, then installing $2k of high quality injectors and getting another 100k from the truck, is possibly the best dollar for dollar value in the entire truck market
Click to expand...
I can’t tell you the condition of the motor/tranny other than it is supposed to be in working condition when pulled.

As for mileage, the 8.1 is around 150k with a brand new tranny (less than 3k miles). The body with the Duramax is 300ish with a duramax/Allison of unknown mileage.

I may mess a little with the Duramax, see if it will reliably run. If not, just dive in, swap against all other suggestion, and post up the non-sense.
 
You're better off swapping the entire harness and ECM/TCM with whatever engine you're going with. There are enough differences to keep them together.

Everything else is a bolt in.

I have both 8.1L and Duramax engines here.

We did an LB7 with 190K miles. New injectors, hopped up CP3, turbo, etc, building to get to about 550hp. When we did the head studs, the cylinders still had the cross hatching. New injectors don't have the same problems as the originals and if the truck's gone past 150k, more than likely has new injectors. Do a lift pump for the CP3 and you have a solid diesel.

To be clear, I love both engines, when they're done right.

You will want to get rid of the EGR on the 8.1L, like GM did late in the production cycle. It's the source of the oil consumption. They're easy to get 400hp/550tq from.
 
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Grendel said:
You're better off swapping the entire harness and ECM/TCM with whatever engine you're going with. There are enough differences to keep them together.

Everything else is a bolt in.

I have both 8.1L and Duramax engines here.

We did an LB7 with 190K miles. New injectors, hopped up CP3, turbo, etc, building to get to about 550hp. When we did the head studs, the cylinders still had the cross hatching. New injectors don't have the same problems as the originals and if the truck's gone past 150k, more than likely has new injectors. Do a lift pump for the CP3 and you have a solid diesel.

To be clear, I love both engines, when they're done right.

You will want to get rid of the EGR on the 8.1L, like GM did late in the production cycle. It's the source of the oil consumption. They're easy to get 400hp/550tq from.
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I appreciate the reply.
I have looked over the frankentruck write up. Good thing I am swapping the tranny and all saw no having to deal with 2 vs 4wd nonsense in the TCM. I was hoping to swap everything short of the BCM. Do the key relearn. And since I have both trucks being fully loaded, I should have all the fuses needed although I will swap the fuse box. I think my biggest hurdle may be the AC stuff if it turns out not to be plug and play.
 
Well quite the turn of events today. Just to see what would happen, I charged the batteries up good, primed the fuel lines, and the thing started up. It still needs a good bit of work under the hood with small stuff, but it looks like the Duramax may stay right where it is after all.
 
Grendel Sterlingfire Projectjunkie

So I had a close friend of mine who used to run a diesel shop and now just works on his own stuff (all he has ever run are Chevy diesels as he worked for Chevy for a while and now fixes up Duramax trucks) come by and check out the truck. Well, the news is up and down.

The good, he said the engine runs pretty smooth and seems to be in great shape just from an external perspective. Well, as we were standing around it, he asked me to pull the oil cap to check blow by if it had any.

Now for the bad news. As soon as I got it off, oil and diesel mixture blew everywhere so there was a good bit of pressure built up in the crankcase. Not sure why it wasn’t coming out of the drain tube if you will. Then soon after that, the truck started pouring really thin oil out from behind the harmonic balancer. Now mind you, I let this thing sit and run for at least 15 minutes yesterday no problem. Today, ran about 5. Zero starting issues. No funny idle. Only thing which it did yesterday too was press the gas (which I didn’t press hard and I never got out of the shop yard) was under very light acceleration, the truck kinda lunged forward like normal but would level off really quick almost like a stall but would go faster like normal if the accelerator was pressed further. He said he thinks one of the injectors are shot. The oil pressure was zero at this time on an aftermarket gauge the PO had placed under the hood. But yesterday the oil level was normal and had ~25 psi at idle. Maybe a tad more.

My first order of operation is drain the oil, put shone cheap 15-40 in it, and see if I get oil pressure back to make sure I didn’t wipe anything out.

After that, what are your thoughts? Should I run something through the injectors to free them in case some bad diesel caused it from sitting? Do I just replace the injectors because even if the do free up, it is only temporary? Do I just pull the motor and swap the 8.1 in and be done with it? If I do the injectors, I would probably do them myself. I asked the opinion of the diesel mechanic (my friend) and he said he likes the Duramax so he would fix it if it was his. But he also said, it would suck to replace injectors just to find out the bottom end was wiped out with diesel in the oil and tan too long since we have no history.
 
You already have trusted guidance.

I'd drop the pan and take a peek.
 
I’m going to check the return lines. They seem to be an issue that would cause the amount of fuel dump I am seeing (it seems too excessive for just an injector or two). Plan to also put a scanner on it and check some of the read outs.
 
Thoughts on this. Here are some videos. Definitely a lot of diesel in the oil. I drained around 3 gallons. Maybe a tad over. Plus whatever had leaked out before.

changed the oil and my oil pressure went to 55-60 at idle. So much better than 0. And all leaks seemed to stop. I know I still have a leak somewhere. But before I tear this open, should I replace the injectors? I’m not seeing the symptoms of injector failure like hard to start, smoke out of the tailpipe (maybe a small puff), running rough at idle. Only thing I see, is diesel in the fuel and maybe under accel in gear, it doesn’t throw me back but comparing this to an 8.1.

Just a lot of money just to throw at a motor for injectors. I am not against replacing them. Just hate to do it just to do it. Maybe the best answer though? If you get new ones, do you get stock or do you get oversized?
 
Well, I changed out the CP3 pump. Talk about a pain.

the fuel is still dumping. And by dumping, we are talking around 2-4 quarts in 10 minutes.

so to get to the lines, I’m going to have to tear off the valve covers. I feel like at that point, I should just change the injectors (if that isn’t the cause of the problem itself).
My question for the more experience:
1) Stock Bosch injectors or oversized?
2) should I install FASS at the same time? (Does it make it that much difference in the life/health if the injectors)

the truck will mainly see daily driving with some towing. I’d like to get 100-150k miles out of the truck. I can’t imagine I’ll do any crazy tune. Will probably have 33-35s on it at least for now. I just want to do this right the first time and not deal with it anymore.
 
As long as ya keep the tune mild, the stock size injectors will do perfectly fine. The FASS style pumps don’t do much in the way of helping injectors, they simply push fuel up to the cp3 to take some strain off of it. So if ya don’t feel like doing the cp3 again… throw a FASS or an Airdog on it.
 
Ok, update. The truck is my new DD with the Duramax still in it.

So a few things I want to address and hoping maybe I can grab some advice from here:
1) runs great and starts great. I put an airdog-100 or something like that on it. Found all the leaks in my soft fuel lines and replaced them. Helped power out now that it isn’t sucking air bubbles. Also replaced the fuel filter/water separator. I may bypass this at some point since it really isn’t needed now. But I do like having the priming capabilities heaven forbid the lift pump fails.
2) after all of that, I still am low on power. It is just a bit sluggish. I have put it on a cheap scanner but can’t get and fuel rail pressure reading or MAP readings. I do know the tubes themselves are working as I pressurized the system last night and no leak down nor any hissing. So it’s not a pipe or clamp. Could be the turbo, could be the wastegate, could be a sensor like MAF. But the MAF on this doesn’t visibly look dirty but I haven’t cleaned them.
3) AC is not working. Everything is plugged in and the compressor works. When I jump the relay, it kicks on and air gets cold. It is not the low pressure switch either as I jumped it with no change. Just can’t get the compressor to kick on with the button.
4) oil pressure sensor is not working. Manual one reads just fine. 25-30 at idle. Just not on the dash and it is a new sensor. May need to look deeper into the wiring harness. My one thing about both of these items is the fact if you put an LB7 from a different year in (which this truck was motor swapped) those are the two things people have trouble with. But this has plugged in just as it should and no wrong harness issues that I know of and it was supposedly out of the same year model truck just a Denali vs sierra (non-Denali package).
5) none of the stupid gauges work like fuel mileage and oil life and what not. Nor does the rear view mirror compass and temp.
6) Tow haul and lockout from OD works on the dash, does nothing at the trans. Only manually shifting gears does. And for being an 03, it seems to only have 4 gears and not 5 in the Allison which is suspicious.

overall I have been happy with it so far. Just a few things i’d like to work on and get fixed.
 
5 is likely bad solder joints. Pull the rear view mirror off and reflow every solder joint. Pull your gauge cluster and do the same, if not it could be the stepper motors. Apparently a common issue on GMT800’s. I’ve fixed both on my 02 just redoing the solder joints. My trans temp gauge doesn’t move and I haven’t tried to troubleshoot it
 
OutlawRider said:
Ok, update. The truck is my new DD with the Duramax still in it.

So a few things I want to address and hoping maybe I can grab some advice from here:
1) runs great and starts great. I put an airdog-100 or something like that on it. Found all the leaks in my soft fuel lines and replaced them. Helped power out now that it isn’t sucking air bubbles. Also replaced the fuel filter/water separator. I may bypass this at some point since it really isn’t needed now. But I do like having the priming capabilities heaven forbid the lift pump fails.
2) after all of that, I still am low on power. It is just a bit sluggish. I have put it on a cheap scanner but can’t get and fuel rail pressure reading or MAP readings. I do know the tubes themselves are working as I pressurized the system last night and no leak down nor any hissing. So it’s not a pipe or clamp. Could be the turbo, could be the wastegate, could be a sensor like MAF. But the MAF on this doesn’t visibly look dirty but I haven’t cleaned them.
3) AC is not working. Everything is plugged in and the compressor works. When I jump the relay, it kicks on and air gets cold. It is not the low pressure switch either as I jumped it with no change. Just can’t get the compressor to kick on with the button.
4) oil pressure sensor is not working. Manual one reads just fine. 25-30 at idle. Just not on the dash and it is a new sensor. May need to look deeper into the wiring harness. My one thing about both of these items is the fact if you put an LB7 from a different year in (which this truck was motor swapped) those are the two things people have trouble with. But this has plugged in just as it should and no wrong harness issues that I know of and it was supposedly out of the same year model truck just a Denali vs sierra (non-Denali package).
5) none of the stupid gauges work like fuel mileage and oil life and what not. Nor does the rear view mirror compass and temp.
6) Tow haul and lockout from OD works on the dash, does nothing at the trans. Only manually shifting gears does. And for being an 03, it seems to only have 4 gears and not 5 in the Allison which is suspicious.

overall I have been happy with it so far. Just a few things i’d like to work on and get fixed.
Click to expand...
What was the source of the diesel in oil?
 
Projectjunkie said:
What was the source of the diesel in oil?
Click to expand...
Honestly, I am building a new shed and just been driving it and changing the oil pretty often.

That said, it is just one of the lines I’m sure that didn’t get torqued down just quite right. I bought hex bolts and new HP lines (ones under the valve covers). If that doesn’t fix it, I’m going to have to pull the cups.

I honestly think the injectors were done not too many miles before I picked it up (not well). So I saved those injectors. I may have them tested one of these days.
 
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